Acrylonitrile polymer composition stabilized with formaldehyde, a substituted phenol, and acetic anhydride, and method of making same



United States Patent ACRYLONITRILE POLYMER COMPOSITION STA- BILIZED WITH FORMALDEHYDE, A SUBSTI- TUTED PHENOL, AND ACETIC ANHYDRIDE, AND METHOD OF MAKING SAME Richard R. Holmes, Bethesda, Md., and Lloyd T. Jenkins,

Decatur, Ala., assignors to The Chemstrand Corporation, Decatur, Ala., a corporation of Delaware No Drawing. Application May 23, 1956 Serial No. 586,660

20 Claims. (Cl. 26032.6)

This invention relates to the stabilization of acrylonitrile polymers and blends thereof. More particularly, it relates to the stabilization of acrylonitrile polymers and blends thereof which have a.tendency to develop color upon standing or application of heat.

The term polymer, as employed in the instant description and claims, is intended to include homopolymers, copolymers, and blends thereof, said polymers containing at least 80 percent by weight of polymerized or copolymerized acrylonitrile in the polymer molecule.

Acrylonitrile polymers containing 80 percent or more of acrylonitrile are generally insoluble in the more common solvents and in those instances where suitable solvents have been found, in order to effect solution, the application of heat is usually necessary. Where heat is employed to effect solutions, from which shaped articles are to be formed, a tan to dark brown color frequently develops in the solutions and therefore is carried over into the product formed therefrom. This color also develops in solutions upon standing for prolonged periods of time.

The mechanism which causes color formation has not been definitely ascertained, although a variety of reasons therefor have been advanced. The presence of metal ions, such as iron, copper and manganese in the solutions may cause the color. The employment of amide compounds as solvents may result in formation of amines when heat is applied and cause color in the compositions. Impurities present in the solvents have also been cited as a cause. Whatever may be the reason for color formation, it results in compositions and products of to prevent undesirable {color formation in acrylonitrile polymer compositions. v

Another object is to minimize color formation when solutions of the acrylonitrilepolymers are permitted to stand for a prolonged period of time or upon application of heat.

It is also an object of the invention to prevent color formation in acrylonitrile polymers at elevated temperatures.

A still further object of the invention is the production of solutions of acrylonitrile polymers and articles produced therefrom having improved color characteristics.

Other objects and advantages will be apparent from a consideration'of the description of the invention which follows hereafter.

115, general, the objects of the invention are accomplished by dissolving the polymer of acrylonitrile in a suitable solvent therefor and preventing or minimizing color formation by the presence in the solution as an inhibiting agent, "a combined reagent comprising formaldehyde, a compound having the general formula,"

. Patented Mar. 11, 195

wherein R is hydrogen, methoxy, ethoxy or an OH group; and acetic anhydride.

The components of the inhibiting agent maybe employed in equal or unequal amounts, any one constituent being present in a range of from 98 to 1 percent in a three component system. The total amount of inhibit ing agent may be employed in a range of about 0.3 to 15 percent, based on the total polymer weight. However, it is preferred that the inhibiting agent of the instant invention be present in a small amount compared to the amount of polymer dissolved. Thus, although the amount is not critical, it is preferred that the inhibiting agent be present in the amount of about 0.3 to 3.0 percent, based on the total weight of the polymer. The inhibiting agent may be added to the solvents before or after the polymer is dissolved therein. The inhibiting agent permits exposure to high temperatures for prolonged standing periods without the development of the objectionable color which usually results in such solutions. The compositions of the instant invention may be prepared in a varying temperature range. For example, the compositions of the instant invention may be prepared by mixing the polymer, a suitable solvent and the inhibiting agent at any temperature or heating the mixture to a temperature up to the boiling point of the;

solvent.

Among the compounds bearing the general formula,

which may be employed in practising the instant invention are phenol, p-methoxy phenol, p-ethoxy phenol, by droquinone, etc.

Among the solvents which may be used in practising the instant invention are N,N-dimethylformamide, N,N- dimethylacetamide, aqueous zinc chloride, sulfuric acid, aqueous nitric acid, aqueous sodium thiocyanate, ethylene carbonate, sulfolane, nitromethane, etc.

The polymeric materials, which may be employed in the practice of the present invention, are polyacrylonitrile, copolymers, including binary and ternary polymers containing at least 80 percent by weight of acrylonitrile in the polymer molecule, or a blend comprising polyacrylonitrile or copolymers comprising acrylonitrile with from 2 to 20 percent of another polymeric material, the blend having an overall polymerized acrylonitrile content of at least 80 percent by weight. While the preferred polymers employed in the instant invention are those containing at least 80 percent of acrylonitrile generally recognized as the fiber-forming acrylonitrile pblymers, it will be understood that the invention is likewise applicable to polymers containing less than 80 percent operations, lacquers, etc., in all of which applications seasons the alleviation of undesirable color is extremely impor- I tent.

For example, the polymer may be a copolymer of from 80 to 98 percent acrylonitrile and from 2 to 20 percent of another monomer containing the C==C linkage and copolymerizable with acrylonitrile. Suitable monoolefinic monomers include acrylic, alpha-chloroacrylic and methacrylic acids; the acrylates, such as methylmethacrylate, ethylmethacrylate, butylmethacry late, methoxyrnethyl methacrylate, beta-chloroethyl methacrylate, and the corresponding esters of acrylic and alpha-chloroacrylic acids; vinyl chloride, vinyl fluoride,

vinyl bromide, vinylidcne chloride, l-chloro-l-bromoethylene; methacrylonitrile, acrylamide and methacrylamide; alpha-chloroacrylamide, or monoalkyl substitution products thereof; methyl vinyl ketone; vinyl carboxylates, such as vinyl acetate, vinyl chloroacetate, vinyl propionate, and vinyl stearate; N-vinylimides, such as N-vinylphthalimide and N-vinylsuccinimide; methylene malonic esters; itaconic acid and itaconic ester; N-vinylcarbazole; Vinyl fnrane; alkyl vinyl esters; vinyl sulfonic acid; ethylene alpha, beta-dicarboxylic acids or their anhydrides or derivatives, such as diethylcitraconate, diethylmesaconate, styrene, vinyl naphthalene; vinyl-substituted tertiary heterocyclic amines, such as the vinylpyridines and alkyl-substituted vinylpyridines, for example, 2-vinylpyridine, 4-vinylpyridine, 2methyl-5- vinylpyridine, etc.; l-vinylimidazole and alkyl-substituted l vinylimidazoles, such as 2-, 4-, or S-rnethyl-l-vinylimidazole, and other C==C containing polymerizable materials.

The polymer may be a ternary interpolymer, for example, products obtained by the interpolyrnerization of acrylonitrile and two or more of any of the monomers, other than aciylonitrile, enumerated above. More specifically, and preferably, the ternary polymer comprises acrylonitrile, methacrylonitrile, and 2-vinylpyridine. The ternary polymers preferably contain from 80 to 97 percent of acrylonitrile, from 1 to. 10 percent of a vinylpyridine or a l-vinylimidazole, and from 1 to '18 percent of another substance, such as methacrylonitrile or vinyl chloride.

The polymer may also be a blend of polyacrylonitrile or of a binary interpolymer of from 80 to 99 percent acrylonitrile and from 1 to percent of at least one other C=C containing substance with from 2 to 50 percent of the weight of the blend of a copolymer of from 10 to 70 percent of acrylonitrile and from to 90 percent of at least one other C,- -C containing polymerizable monomer. Preferably, when the polymeric material comprises a blend, it will be a blend of a copolymer of 90 to 98 percent. acrylonitrile and from 2 to '10 percent of another mono-olefinic monomer, such as vinyl acetate, which is not receptive to dyestuif, with a s'utlicient amount of a copolymer of from 10 to 70 percent of acrylonitrile and from 30 to 90 percent of a vinyl-substituted tertiary heterocyclic amine, such as vinylpyridine or l-vinylimidazole, to give a dyeable blend having an overall vinyl-substituted tertiary heterocyclic amine content of from '2 to 10 percent, based on the weight of the blend,

The polymers, useful in the practice of the present invention, may be prepared by any conventional polymerization procedures, such as mass polymerization methods, solution polymerization methods, or aqueous emulsion procedures. However, the preferred practice utilizes suspension polymerization wherein the polymer is prepared in finely divided form for immediate use in the fiber fabrication operations. The preferred suspension. polymerization may utilize batch procedures, wherein monomers are charged with an aqueous medium containing the necessary catalyst and dispersing agents. A more. desirable method involves the semi-continuous procedure in which the polymerization reactor containing the. aqueous medium. is charged. with the desired monomers and the continuous withdrawal of polymer may also be employed.

The polymerization is catalyzed by means of any water-soluble peroxy compound, for example the potassium, ammonium and other water-soluble salts of peroxy acids, sodium peroxide, hydrogen peroxide, sodium perborate, the sodium salts of other peroxy acids, and any other water-soluble compound containing a peroxy group (O-O-) A wide variation in the quantity of peroxy compound is possible. For example, from 0.1 to 3.0 percent by weight of the polymerizable monomer may be used. The catalyst may be charged at the outset of the reaction, or it may be added continuously or in increments throughout the reaction for the purpose of main taining a more uniform concentration of catalyst in the reaction mass. The latter method is preferred because it tends to make the resultant polymer more uniform in its chemical and physical properties.

Although the uniform distribution of the reactants throughout the reaction mass can be achieved by vigorous agitation, it is generally desirable to promote the uniform distribution of reagents by using inert Wetting agents, or emulsion stabilizers. Suitable reagents for this purpose are the water-soluble salts of fatty acids, such as sodium cleate and potassium stearate, mixtures of water-soluble fatty acid salts, such as common soaps prepared by the saponification of animal and vegetable oils, the amino soaps, such as salts of triethanolamine and dodecylmethylamine, salts of rosin acids and mixtures thereof, the water-soluble salts of half esters of sulfuric acid and long chain aliphatic alcohols, sulfonated hydrocarbons, such as alkyl aryl sulfonates, and any other of a wide variety of wetting agents, which are in general organic compounds containing both hydrophobic and hydrophilic radicals. The quantity of emulsifying agents will depend upon the particular agents selected, the ratio of monomer to be used, and the conditions of polymerization. In general, however, from 0.01 to 1.0 percent by weight of the monomers may be employed.

The emulsion polymerizations are preferably conducted in glass or glass-lined vessels which are provided with a means for agitating the contents. Generally rotary stirring devices are the most effective means of insuring the intimate contact of the reagents, but other methods may be successfully employed, for example by rocking or tumbling the reactors. The polymerization equipment generally used is conventional in the art and the adaptation of a particular type of apparatus to the reaction contemplatedis within the province of one'skilled in the art. The articles manufactured therefrom may be produced by well-known conventional methods, for example, the wet-spinning, dry-spinning and melt-spinning methods for producing fibers. j

The following examples are illustrative rather than limitative and all parts, proportions and percentages are by weight unless otherwise specified.

EXAMPLE I 7.5 grams of a polymer blend of 88 percent of a ct polymer containing 94 percent of acrylonitrile and 6 percent of vinyl acetate and 12 percent of a copolymer of 50 percent of acrylonitrile and 50 percent of Z-methyl-S- vinyl pyridine were added to 45 milliliters of N,N-dimethylacetarnide containing approximately 0.05 gram of titanium dioxide. The mixture was stirred and heated to 70 C. It was then quickly cooled to room temperature and the color measured. This sample was used as 80011? trol. The purity is set forth below. Subsequently, like samples were prepared but with 0.225 gram of a color inhibitor containing 0.075 gram each of formaldehyde, phenol and acetic anhydride; formaldehyde, p-methoxy phenol and acetic anhydride; and formaldehyde, hydroquinone and acetic anhydride. The purity is set forth below.

EXAMPLE II 7.5 grams of a copolymer containing 94 percent of acrylonitrile and 6 percent of vinyl acetate were added to 45 milliliters of N,N-dimethylacetamide containing approximately0.05 gram. of titanium dioxide. The mixture was stirred and heated for 35 minutes at 70 C. It was then quickly cooled to room temperature and the color measured. This sample was used as a control. The purity is set forth below. Subsequently, like samples were prepared but with 0.225 gram of an inhibiting agent containing 0.075 gram each of formaldehyde, p-methoxy phenol and acetic anhydride; and formaldehyde, hydroquinone and acetic anhydride. The purity is set forth below.

l p EXAMPLE III 7.5 grams ofan acrylonitrile homopolymer were added to 45 milliliters of N,N-dimethylacetamide containing approximately 0.05 gram of titanium dioxide. The mixture was stirred and heated for 50 minutes at 90 C. It was .then quickly cooled to room temperature and the color measured. This sample was used as a control. The purity of the control sample is set forth below. Subsequently, like samples were prepared but with 0.225 gram of an inhibiting agent containing 0.075 gram each of formaldehyde, p-methoxy phenol and acetic anhydride; and formaldehyde, hydroquinone and acetic anhydride. The purity is set forth below.

The tests for color indicative of approaching whiteness used throughout the examples consist of measurements of purity as calculated from the tristimulus values determined on a General Electric spectrophotometer by the methods recommended by the Standard Observer and Coordinate System of the International Commission on 11- lumination, as fully set forth in the Handbook of Colorimetry published by The Technology Press, Massachusetts Institute of Technology in 1936.

The compositions of the instant invention present many advantages. For example, products formed from the polymer solutions of the instant invention are free of objectionable color and therefore of greater commercial value. In preparing the polymer solutions, heat may be applied without the danger of color formation and the solutions, if necessary, may stand for prolonged periods and remain free of color. The inhibiting agents are readily available and inexpensive. Therefore,- no great increase in production cost is necessary. The compositions containing the inhibitors may be prepared without going through detailed and elaborate procedures that necessitate expensive changes in the design of the ap paratus used to manufacture them.

It will be understood to those skilled in the art that many apparently widely different embodiments of this invention can be made without departing from the spirit and scope thereof. Accordingly, it isto be understood that this invention is not to be limited to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. A new composition of matter comprising a polymer containing in polymerized form at least percent of acrylonitrile and up to 20 percent of another polymerizable mono-olefinic monomer copolymerizable therewith, a solvent therefor, and an inhibiting agent containing sub, stantially equal proportions by weight of formaldehyde, a compound having the general formula,

wherein R is selected from the group consisting of hydrogen, methoxy, ethoxy and hydroxyl radicals; and acetic anhydride.

2. A new composition of matter as defined in claim 1 wherein the polymer is a copolymer containing from 80 to 98 percent of acrylonitrile and from 2 to 20 percent of another polymerizable mono-olefinic monomer copolymerizable therewith.

3. A new composition of matter as defined in claim 1 wherein the polymer is a blend of 80 to9 9 percent of (A) a copolymer containing to 98 percent of acrylonitrile and2 to 10 percent of vinyl acetate and 1 to 20 percent of (B) a copolymer containing 10 to 70 percent of acrylonitrile and 30 to 90 percent of Z-methyl-S-vinyl pyridine.

4. A new composition of matter as defined in claim 3 wherein the compound is phenol.

5. A new composition of matter as defined in claim 1 wherein the polymer is polyacrylonitrile.

6. A new composition of matter as defined in claim 1 wherein the compound is p-methoxy phenol.

7. A new composition of matter as defined in claim 1 wherein the compound is p-ethoxy phenol.

8. A new composition of matter as defined in claim 1 wherein the compound is hydroquinone.

9. A new composition of matter as defined in claim 1 wherein the solvent is N,N-dimethylacetamide.

10. A new composition of matter comprising a copolymer containing in polymerized form 80 to 98 percent of acrylonitrile and 2 to 20 percent of vinyl acetate, a solvent therefor, and 0.3 to 15 percent, based on the total weight of the polymer, of an inhibiting agent, said inhibiting agent containing substantially equal proportions by weight of formaldehyde, a compound having the general formula,

11,. A new composition of matter comprising a polymer wherein R is selected from the group consisting of hydrogen, methoxy, ethoxy and hydroxyl radicals; and acetic anhydride.

12. A new composition of matter comprising polyacrylonitrile, a solvent therefor, and 0.3 to 15 percent, based on the total weight of the polymer, of an inhibiting agent, said inhibiting agent containing substantially equal proportions by weight of formaldehyde, a compound having the general formula,

wherein R is selected from the group consisting of hydrogen, methoxy, ethoxy and hydroxyl radicals; and acetic anhydride.

I 13. A method for preparing a new composition of matter comprising mixing a polymer containing in polymerized form at least 80 percent of acrylonitrile, a solyent therefor, and an inhibiting agent containing sub- 5;? stantially equal proportions by weight of formaldehyde, a compound having the general formula,

wherein R is selected from the group consisting of hydrogen, methoxy, ethoxy and hydroxyl radicals; and acetic anhydride; and heating the mixture to form a homogeneone solution. I

14. The method as defined in claim 13 wherein the polymer is a copolymer containing from to 98 percent of acrylonitrile and from 2 to 20 percent of another polymerizable mono-olefinic monomer copolymerizable therewith.

15. The method as defined in claim 13 wherein the polymer is a blend of 80 to 99 percent of (A) a copolymer containing to 98 percent of acrylonitrile and.2 to 20 percent of vinyl acetate and 1 to 20 percent of (B) a copolymer containing 10 to 70 percent of acryonitrile and 30 to 90 percent of 2-methyl-5-vinyl pyridine.

16. The method as defined in claim 15 wherein the compound is phenol.

17. The method as defined in claim 13 wherein the polymer is polyacrylonitrile.

18. The method as defined in claim 13 wherein the compound is p-mcthoxy phenol.

19. The method as defined in claim 13 wherein the compound is p-ethoxy phenol.

20. The method as defined in claim 13 wherein the compound is hydroquinone.

References Cited in the file of this patent UNITED STATES PATENTS 2,502,030 Scheiderbauer Mar. 28, 1950 2,689,236 Webb Sept. 14, 1954 2,730,436 Young et a1 I an. 10, 1956 

1. A NEW COMPOSITION OF MATTER COMPRISING A POLYMER CONTAINING IN POLYMERIZED FORM AT LEAST 80 PERCENT OF ACRYLONITRILE AND UP TO 20 PERCENT OF ANOTHER POLYMERIZABLE MONO-OLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, A SOLVENT THEREFOR, AND AN INHIBITING AGENT CONTAINING SUBSTANTIALLY EQUAL PROPORTIONS BY WEIGHT OF FORMALDEHYDE, A COMPOUND HAVING THE GENERAL FORMULA, 